1. Field of the Invention
The present invention relates to an Electro Static Discharge (ESD) protection component that protects an electronic device against static electricity.
2. Description of Related Art
The withstand voltage of an electronic part used for an electronic device is becoming low with a rapid progress in downsizing and higher performance of an electronic device such as a mobile phone. Consequently, the number of failures is increasing where static pulses occurring when a human body touches a terminal of an electronic device destroy an electronic part inside the electronic device.
Conventionally, the following method has been well known for protecting the electronic device from such static pulses. A laminated chip varistor or Zener diode is provided between a line to which static electricity is input and the ground, to bypass static electricity for suppressing a voltage applied to an electronic part inside an electronic device.
In addition, a growing number of antistatic areas against static pulses are seen with size reductions and higher performance of electronic devices. Consequently, demand for antistatic measures is particularly increasing for a component with a plurality of parts arranged in an array, as well as for a single part. Further, demand for downsizing and slimming down is also increasing recently.
One Electro Static Discharge (ESD) protection component that meets the demand for downsizing, arraying, and slimming down is a varistor. A method of manufacturing the varistor is disclosed in Japanese Patent Laid-Open Application No. S63-316405. The method discloses a step of screen-printing a varistor paste made of varistor powder and a glass component on one surface of a baked ceramic substrate to form a varistor pattern, and then baking it. In addition, using alumina or the like, with a high mechanical strength, for the ceramic substrate allows an ESD protection component that meets a demand for arraying and slimming down to be implemented.
Generally, it is known that the arrangement structure of particles after baking largely influences the varistor characteristic. This characteristic appears owing to the existence of an insulating layer at grain boundaries of semiconductor particles such as zinc oxide that is the principal component of a varistor. In a case where formed with screen printing, the percentage of varistor content in the paste must be small if the pattern shape is to be printed with a high degree of accuracy. Still, the uniformity of the varistor particles in the paste is not so great.
Therefore, a large number of cracks and holes occur inside a varistor film formed with conventional screen-printing, and areas without insulating films at grain boundaries of semiconductor particles like zinc oxide will increase as well. Thus, a high-performance varistor characteristic cannot be achieved with screen printing. In addition, the varistor characteristic is not uniform, which reduces reliability.